1. Field of the Invention
The present invention relates to an image transmission system and an image transmission method of sending an image generated by an information processing apparatus such as a personal computer (hereinafter abbreviated as “PC”) to a display controlling apparatus such as a projector.
2. Description of the Related Art
Recently, projectors that project image signals received from PCs onto screens are often used when presentations are given at conferences and seminars.
Image signals are sent and received between a PC and a projector generally by establishing an analog connection using an analog RGB cable. Now, attention has been paid to an image transferring system that connects a PC to a projector via a network, because of the following reasons: it is bothersome to establish an analog connection; it is difficult to establish a connection from a remote place; and there is a need to connect multiple PCs to a projector.
In order to realize this image transferring system, so-called screen capturing has been periodically performed on a screen displayed on an image processing apparatus such as a PC, and image data obtained by the screen capturing has been sent to a display apparatus such as a projector.
In the above-described image transferring system, a delay time occurs until the screen captured by using the PC is transmitted to a network and the transmitted screen data is displayed on the projector. When the delay time becomes longer, the user feels uncomfortable when operating the PC while looking at the projector. It thus becomes necessary to reduce the delay time. When the screen is to be captured at certain intervals, even images where the screen is unchanged are sent. Since such redundant images are sent, the delay time is increased. Therefore, the screen capturing is generally performed at a timing at which the screen of the PC is updated.
Japanese Patent Laid-Open No. 2006-262116 discloses a method of monitoring the most recent screen stored in a screen storage unit and the subsequent screen stored in a video memory by using a screen change monitoring unit. When it is determined that the most recent screen is changed, the screen stored in the video memory is captured, and the captured screen is sent from an image sending unit via a network to an image receiving apparatus.
Normally, an image obtained by capturing the screen by using a PC is, for example, compressed and sent to a display apparatus. The display apparatus, which has received the compressed image data, decodes the compressed image data and displays the decoded image data. In general, a display apparatus whose processing rate is low takes time to decode data. Therefore, when an image captured after the screen has been updated is sent from the PC, the display apparatus is still decoding the previous image. It takes time for the display apparatus to be ready to process the received image. As a result, data transfer is not efficiently performed, and a delay time until the screen captured by the PC is actually displayed on the display apparatus is increased.